Weezer have lost their bassist, and they have no idea where to find him.

Bass player Mikey Welsh missed a plane flight late Tuesday night to join the band for a video shoot, according to band assistant Karl Koch, who had said earlier that Welsh was suffering from a "private medical condition."

As of Wednesday morning (August 15), Welsh hadn't told his bandmates where he was or why he missed his flight, Koch wrote on the band's official Web site (www.weezer.com).

"At this point, we are wondering if either ... Mikey is in worse shape than we thought (but we still don't know the nature of what could be troubling him, and no one close to him is passing along any such info)," Koch wrote. "Or ... Mikey has chosen not to come on purpose. Without any word from anyone close to the matter, we are about as much in the dark as the fans on this one, and are forced to speculate."

A spokesperson for Weezer's label, Interscope, had no comment on Welsh.

Weezer were set to spend Wednesday filming a new video for "Island in the Sun" with director Spike Jonze, according to Koch.

In May, Welsh said that he and his bandmates were close friends and called frontman Rivers Cuomo "a sweetheart."

Welsh said that, like Cuomo, he preferred to separate his public and private personas. "[Rivers] keeps his guard up like we all do, because you usually have people trying to take things from you, like your sanity or whatever. People are trying to pick little parts of you off all the time. It's nice to be able to hide and protect yourself because people definitely do like to pick you apart.

"If [Rivers] is nuts, we're all nuts," Welsh continued, laughing. "That must be the reason we all get along. ... We get along very well."